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Subject[PATCH 2/5] x86/mpx: remove build infrastructure
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From: Dave Hansen <dave.hansen@linux.intel.com>

MPX is being removed from the kernel due to a lack of support
in the toolchain going forward (gcc).

Remove the Kconfig option and the Makefile line. This makes
arch/x86/mm/mpx.c and anything under an #ifdef for
X86_INTEL_MPX dead code.

Cc: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: x86@kernel.org
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
---

b/arch/x86/Kconfig | 28 ----------------------------
b/arch/x86/mm/Makefile | 1 -
2 files changed, 29 deletions(-)

diff -puN arch/x86/Kconfig~mpx-remove-build arch/x86/Kconfig
--- a/arch/x86/Kconfig~mpx-remove-build 2020-01-23 10:41:04.863942440 -0800
+++ b/arch/x86/Kconfig 2020-01-23 10:41:04.869942440 -0800
@@ -1896,34 +1896,6 @@ config X86_INTEL_UMIP
specific cases in protected and virtual-8086 modes. Emulated
results are dummy.

-config X86_INTEL_MPX
- prompt "Intel MPX (Memory Protection Extensions)"
- def_bool n
- # Note: only available in 64-bit mode due to VMA flags shortage
- depends on CPU_SUP_INTEL && X86_64
- select ARCH_USES_HIGH_VMA_FLAGS
- ---help---
- MPX provides hardware features that can be used in
- conjunction with compiler-instrumented code to check
- memory references. It is designed to detect buffer
- overflow or underflow bugs.
-
- This option enables running applications which are
- instrumented or otherwise use MPX. It does not use MPX
- itself inside the kernel or to protect the kernel
- against bad memory references.
-
- Enabling this option will make the kernel larger:
- ~8k of kernel text and 36 bytes of data on a 64-bit
- defconfig. It adds a long to the 'mm_struct' which
- will increase the kernel memory overhead of each
- process and adds some branches to paths used during
- exec() and munmap().
-
- For details, see Documentation/x86/intel_mpx.rst
-
- If unsure, say N.
-
config X86_INTEL_MEMORY_PROTECTION_KEYS
prompt "Intel Memory Protection Keys"
def_bool y
diff -puN arch/x86/mm/Makefile~mpx-remove-build arch/x86/mm/Makefile
--- a/arch/x86/mm/Makefile~mpx-remove-build 2020-01-23 10:41:04.865942440 -0800
+++ b/arch/x86/mm/Makefile 2020-01-23 10:41:04.870942440 -0800
@@ -45,7 +45,6 @@ obj-$(CONFIG_AMD_NUMA) += amdtopology.o
obj-$(CONFIG_ACPI_NUMA) += srat.o
obj-$(CONFIG_NUMA_EMU) += numa_emulation.o

-obj-$(CONFIG_X86_INTEL_MPX) += mpx.o
obj-$(CONFIG_X86_INTEL_MEMORY_PROTECTION_KEYS) += pkeys.o
obj-$(CONFIG_RANDOMIZE_MEMORY) += kaslr.o
obj-$(CONFIG_PAGE_TABLE_ISOLATION) += pti.o
_
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